From 322eea1af5a182c840877913238183fd445e3fb4 Mon Sep 17 00:00:00 2001
From: Bob Nystrom <robert@stuffwithstuff.com>
Date: Thu, 26 Mar 2015 07:17:09 -0700
Subject: [PATCH] Generate a runtime error if a foreign method was not found.

---
 src/vm/wren_vm.c                              | 21 +++++++++++++++++--
 .../foreign/foreign_after_static.wren         |  3 +++
 .../foreign/foreign_method_with_body.wren     |  3 +++
 test/language/foreign/unknown_method.wren     |  3 +++
 4 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 test/language/foreign/foreign_after_static.wren
 create mode 100644 test/language/foreign/foreign_method_with_body.wren
 create mode 100644 test/language/foreign/unknown_method.wren

diff --git a/src/vm/wren_vm.c b/src/vm/wren_vm.c
index 1c21686d..61031f9c 100644
--- a/src/vm/wren_vm.c
+++ b/src/vm/wren_vm.c
@@ -312,7 +312,14 @@ static WrenForeignMethodFn findForeignMethod(WrenVM* vm,
   return NULL;
 }
 
-static void bindMethod(WrenVM* vm, int methodType, int symbol,
+// Defines [methodValue] as a method on [classObj].
+//
+// Handles both foreign methods where [methodValue] is a string containing the
+// method's signature and Wren methods where [methodValue] is a function.
+//
+// Returns an error string if the method is a foreign method that could not be
+// found. Otherwise returns `NULL_VAL`.
+static Value bindMethod(WrenVM* vm, int methodType, int symbol,
                        ObjModule* module, ObjClass* classObj, Value methodValue)
 {
   Method method;
@@ -324,6 +331,13 @@ static void bindMethod(WrenVM* vm, int methodType, int symbol,
                                           classObj->name->value,
                                           methodType == CODE_METHOD_STATIC,
                                           name);
+
+    if (method.fn.foreign == NULL)
+    {
+      return wrenStringFormat(vm,
+          "Could not find foreign method '@' for class $ in module '$'.",
+          methodValue, classObj->name->value, module->name->value);
+    }
   }
   else
   {
@@ -341,6 +355,7 @@ static void bindMethod(WrenVM* vm, int methodType, int symbol,
 
   if (methodType == CODE_METHOD_STATIC) classObj = classObj->obj.classObj;
   wrenBindMethod(vm, classObj, symbol, method);
+  return NULL_VAL;
 }
 
 static void callForeign(WrenVM* vm, ObjFiber* fiber,
@@ -1219,7 +1234,9 @@ static bool runInterpreter(WrenVM* vm)
       uint16_t symbol = READ_SHORT();
       ObjClass* classObj = AS_CLASS(PEEK());
       Value method = PEEK2();
-      bindMethod(vm, instruction, symbol, fn->module, classObj, method);
+      Value error = bindMethod(vm, instruction, symbol, fn->module, classObj,
+                               method);
+      if (IS_STRING(error)) RUNTIME_ERROR(error);
       DROP();
       DROP();
       DISPATCH();
diff --git a/test/language/foreign/foreign_after_static.wren b/test/language/foreign/foreign_after_static.wren
new file mode 100644
index 00000000..9bb91c4a
--- /dev/null
+++ b/test/language/foreign/foreign_after_static.wren
@@ -0,0 +1,3 @@
+class Foo {
+  static foreign method // expect error
+}
diff --git a/test/language/foreign/foreign_method_with_body.wren b/test/language/foreign/foreign_method_with_body.wren
new file mode 100644
index 00000000..aaff1e3a
--- /dev/null
+++ b/test/language/foreign/foreign_method_with_body.wren
@@ -0,0 +1,3 @@
+class Foo {
+  foreign method { "body" } // expect error
+}
diff --git a/test/language/foreign/unknown_method.wren b/test/language/foreign/unknown_method.wren
new file mode 100644
index 00000000..9b7c7c45
--- /dev/null
+++ b/test/language/foreign/unknown_method.wren
@@ -0,0 +1,3 @@
+class Foo {
+  foreign someUnknownMethod // expect runtime error: Could not find foreign method 'someUnknownMethod' for class Foo in module 'main'.
+}